Obesity rates among American Indian (AI) children are the highest of any race or ethnic group in the United States. Once established, early obesity persists into later life and greatly increases risk of future chronic diseases such as cardiovascular disease and type 2 diabetes. Healthy Children, Strong Families (HCSF) is a community-based, multimodal, early childhood intervention which addresses the growing problem of AI childhood obesity. HCSF directly involves parents/ primary caregivers of preschool age AI children in making family based healthy lifestyle changes. An initial small HCSF trial showed promise in reducing adult BMI and child BMI z-score in overweight/obese AI children, increasing adult/child fruit/vegetable intake, decreasing TV/screen time, and increasing adult self-efficacy for healthy behavior change. The proposed study will use community-based participatory research methods to enhance the intervention and then conduct a 2-arm staggered-enrollment randomized trial of HCSF vs. control (child safety intervention) in a 2-year design in 6 diverse rural and urban AI communities nationally. Intervention outcomes will be measured at 0, 6, 12, 18, and 24 months. Primary outcomes are adult BMI and child BMI Z-score. Secondary outcomes include adult/child waist circumference, fruit/vegetable and added sugar intake, TV/screen time, activity, sleep, home environment changes, and adult psychosocial factors (stress/depression) and use of social networking. Communities will work with investigators to enhance the previously tested HCSF intervention to include novel methods of delivery (mailed lesson kits with cell phone coaching/ social networking) and two less-studied obesity determinants (sleep and stress) to increase impact and sustainability. The research addresses four key gaps in obesity prevention studies: pre-school age families, social networking support, stress and sleep. Aim 1 will test the effectiveness of the HCSF intervention in preventing and reducing obesity among AI parents/primary caregiver(s) and their children (ages 2-5 years) at 12 and 24 months. Aim 2 will identify key mediators of the effect of HCSF on obesity and health behaviors, which may then be utilized in focusing future family-based intervention design. Aim 3 will evaluate the impact of the CBPR process on implementation and local intervention sustainability in each of the six diverse AI communities. The short term goal for this research is to develop a successful obesity intervention for AI families that is practical and easily replicated. The long-term goal is to disseminate the intervention by incorporating HCSF into AI health programs to ensure local sustainability and utility nationally. In terms of public health impact, if the hypotheses are proven, HSCF will be the first evidence-based, culturally adapted, healthy lifestyles intervention for AI families with young children that addresses the obesity epidemic. If successful, it will assist communities in preventing and reducing obesity, and thereby, impact the high and increasing rates of chronic disease in both urban and rural AI communities.